Dynamic pumps are most widely used for high-pressure applications. These pumps have a high efficiency compared to positive displacement pumps. There are many types of dynamic pumps, and an axial flow pump is one of them. According to the flow of working fluid, dynamic pumps have two major types:
- Centrifugal radial flow pump
- Axial flow pump
The centrifugal pumps have an inflow of the fluid perpendicular to the impeller, while the axial pumps have a parallel suction flow of fluid to the axis of the impeller. In the previous article, we discussed radial flow centrifugal pumps. Therefore, in this article, I am just going to explain the axial flow pump deeply.
What is Axial flow Pump?
An axial flow pump is a type of dynamic pump which has a suction parallel to the impeller direction. An axial flow pump doesn’t change the flow direction of the fluid. In this pump, the fluid enters and exits the pump in the parallel direction to the impeller. It has an impeller inside the pipe. This pump has three to four blades that are installed on the impeller.
The pump blades design in such a way that the pump discharges the water axially in the parallel direction to the impeller nor perpendicular. The parallel alignment of the impeller blades creates a very low pressure when pumping water. These pumps use for high flow rate and low pressure applications.
These dynamic pumps can generate high flow rates, up to hundreds of thousands of gallons per minute. It is sometimes called a propeller pump because the axial impeller is similar to a ship’s propeller. In some configurations, the flow rate and head can be adjusted by changing the pitch of the impeller blades.
The functional specifications of the axial pumps are a little bit different than other types of pumps. The head produced at normal operating points is minimal, but the curve of head versus capacity is considerably vertical than other dynamic pumps. The shut-off pressure can be three times the pump’s delivery head at the point with the greatest efficiency. Besides, the required power rises when the flow rate declines, and the maximum power consumption is with the power switched off (zero flow). This contrasts with the same tendency for the radial-pump, which requires higher flow rates and higher power.
Working Principle of Axial Flow Pump
In the axial flow pump, the impeller blades guide the fluid axially. In this pump, the pressure generates by passing the fluid over the impeller vanes. In these dynamic pumps, the impeller vanes have an airfoil section through which fluid runs and creates pressure.
The liquid pushes in the direction of the axis of rotation of the impeller. That is, the fluid particles do not transform their radial position as they flow through the pump. This permits the liquid to flow axially into the impeller and to exit the fluid approximately axially. The propellers of these dynamic pumps drive through an electric motor.
The required power increases with a decreasing flow rate, and the maximum power is drawn at a zero-flow rate. While in the case of the centrifugal radial-pump, this feature is the opposite, in which power requirements increase with increasing the flow rate. The power requirements and pump heads also increase as the slope increases to adjust the pump to system conditions for the most efficient operation.
Compared to conventional centrifugal or radial pumps, axial pumps can pump up to three times more liquids with a delivery head of fewer than 4 meters. By changing the propeller pitch, you can easily set these dynamic pumps to run with maximum efficiency at high or low pressure and low/high pressure.
The axial flow pump generally has a low head than radial pumps but can generate higher currents. Axial flow pumps can only produce heads of 10 to 20 feet. This is lower as compared to other types of centrifugal pumps.
How to select an Axial Pump
If you want to buy an axial flow pump, then keep in mind the following specifications to choose the best suitable pump:
- Flow Rate: The speed at which liquids flow by the pump (gallons/minute (GPM)) is known as flow rate. To choose a pump, you must know the fluid flow rate that you want to pump because nominal capacity and pump flow rate must match for a smooth process.
- Pressure: Pressure is another significant factor that you need to keep in mind for choosing a pump. Choose a pump that may handle your fluid pressure according to your desire.
- Head: It is a height from the inlet area to the discharge area. It describes in feet or meters. Choose a pump that can pump fluid up to your desired head.
- Net Positive Suction Head (NPSH): The pressure difference between the pump inlet heads and the vapor head is known as NPSH. This term calculates to prevent cavitation issues.
- Output power: The absolute power generated by the pump is known as output power. Choose an axial flow pump according to your desired output power.
- Input power: the energy required to run the pump.
- Efficiency: It is a ratio of input power to output power. The efficiency defines the amount of input energy used for pumping. It is another important factor that must be kept in mind for choosing a pump.
Applications of Axial Pump
- These dynamic pumps largely use in different industries all over the world.
- These pumps use for handling sewage by fisheries, agriculture, municipal and commercial.
- Axial flow pump uses in digesters and powerplants for circulating fluids.
- This type of dynamic pump uses for low heads and high flow rate applications.
- They use in the chemical industries for the circulating of fluids in the evaporator.
- In sailboats, these used for transferring pumps that use for sailing ballast.
Advantages and disadvantages of Axial Pump
An axial pump has the following major advantages and disadvantages:
Advantages of Axial flow Pumps
- The main advantage of axial pumps is that they have a relatively low head and a relatively high flow rate.
- These dynamic pumps are ideal for l high flow rate and low head.
- With axial pumps, the effects of fluid turning are less severe.
- Axial pumps can easily be set up for low flow and high head for high-efficiency operation.
- Of the many conventional pumps, these pumps are the smallest.
- The small size makes it easy to use and handle.
Disadvantages of Axial flow Pumps
- These pumps have a high cost.
- These pumps can’t control liquids having high viscosity.
- They are not best for applications where require a high head.
Difference between Centrifugal Pump and Axial Flow Pump:
|Sr.||Centrifugal Pump||Axial Flow Pump|
|1.||In a centrifugal pump, the flow of the liquid is radial to the shaft of the impeller.||In these, the flow of liquid is parallel to the impeller shaft.|
|2.||They are best for high-head applications.||They are best for low-head applications.|
|3.||They have a large size as compared to axial pumps.||They have small in size.|
|4.||They are not too easy to control.||They are easy to control.|
In this article, we study the axial flow pump and its working principle. Axial pumps are widely using in different industries. These pumps get preference over the centrifugal radial pumps.